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Shahin Sheikh-Jabbari
IPM, Tehran

What is your name, affiliation, academic position, and job title?
My name is Mohammad M. Sheikh-Jabbari (known as Shahin Sheikh-Jabbari).
Professor of physics at Institute for Research in Fundamental Sciences (IPM), Tehran, Iran since 2005.

What is your journey? (Where did you live, learn and work?)
I received my PhD in February 1998 (at the age of 24) from Sharif University in Tehran.
I was a postdoc at IPM (my current institute) from March 1998 until September 1999. Then I joined ICTP, in Trieste, Italy as a postdoc (Oct 1999-Oct 2001), followed by another postdoc at Stanford University (Oct 2001-Oct 2004). I also visited ICTP/SISSA from October 2004 until January 2005.
In January 2005 I joined IPM as an associate professor and I am a full professor at IPM since July 2006.

What is your field of research and/or what project are you involved in? Briefly describe your career trajectory to date. What positions have you held, when and where?
In the over 25 years that I have been working as a researcher in physics, I have followed various research interests in the area of theoretical physics, particle physics and cosmology. Here is a short account:
During my PhD and postdocs my focus was mainly on theoretical high energy physics, while I also occasionally worked on related areas in particle physics and cosmology. I was among the first people who uncovered noncommutative structure on D-branes in a background NSNS field. Together with Michael Peskin and Stephon Alexander in 2004 we proposed a novel leptogensis model which operates during inflation.
Since 2008 and with the new CMB observations WMAP and then by Planck mission, I also worked on early Universe cosmology. Among other things, I proposed the gauge-flation which is an inflationary model driven by non-Abelian gauge fields (instead of the usual scalar fields).
One of my interests, especially in the last 10-15 years has been theoretical (semiclassical and quantum) aspects of black holes. A part of my experience in this field, besides the research papers, has been gathered in a graduate textbook “Black Holes, from collapse to evaporation” (co-authored with Daniel Grumiller), published by Springer in November 2022.
In the last 3-4 years, I have also worked on tension in Lambda-CDM cosmology and have noted a novel feature: non-constancy (e.g., redshift dependence) of cosmological parameters signals breakdown of a cosmological model (like Lambada-CDM).

What are your research plans?
Currently I am following three different research programs:
Semiclassical aspects of black holes. I have put forward a new “semiclassical quantization” of black holes, where degrees of freedom residing at the horizon are treated quantum mechanically and the bulk gravity modes are classical. The hope is that this setup can address questions regarding black hole microstates and black hole information problem.
Cosmological tensions and how to understand them. There is a growing consensus that tensions in the standard model of cosmology, in particular H0 and S8 tensions, are not due to systematics and are pointing to a beyond standard model physics. There are MANY papers trying to address these tensions. However, I believe that, before attempting to resolve the tensions, one should try to understand the tensions better, what they mean and imply, and what exactly is wrong with the Lambda-CDM model which has led to the tensions.
Dipole Cosmology setup. There are various hints that there is a preferred direction in the sky and that one may need to go beyond the usual FLRW framework. We have recently proposed the dipole cosmology setup which allows for non-kinematical dipole in CMB and/or in the distribution of matter or structure in the Universe. Developing this framework, theoretically and phenomenologically and comparing it to observations is what we are engaged in.

How does CosmoVerse fit within those plans?
CosmoVerse is in line with my cosmological interests. It is a nice platform for discussing my ideas and results with peers and helps with having fruitful scientific discussions in the area of cosmology close to my interests.

Which of your skills are you most proud of, or find most useful?
I view myself primarily as a theorist. I have a lot of experience in various areas of theoretical physics and also have good analytical skills.

What new skills would you like to learn in the next year?
I would like to learn more about basics of statistical methods in cosmological data fitting.

What are the most exciting open questions in your research area?
Statistical origins of black hole thermodynamics, microstates of black hole.
Black hole information problem.
What do cosmological tensions tell us about the evolution of the Universe?
How well is cosmological principle tested?

What advances or new results are you excited about or looking forward to?
Cosmological tensions pointing to new physics beyond the standard model of cosmology.
Establishing signatures of cosmic anisotropy.
Formulating black hole microstate problem through boundary (horizon) degrees of freedom.

What is your view on cosmic tensions? How does your work connect with this open question in the community?
In the last decade or so cosmological tensions within the Lambda-CDM model has grown, their statistical significance has grown (to over 5 sigma level) and various different sources of systematics have been ruled out. I believe, H0 tension is real and physical, and it points to new physics beyond Lambda-CDM. On the other hand, I do not think that early resolutions (e.g., EDE) or playing with dark energy in the late Universe can address H0 tension; it is more resilient than finding a resolution only in late or early dark energy sector. S8 tension is not yet at the same level as H0 tension, and it yet remains to establish itself beyond systematics. I give a lower weight to it. In my work, I am trying to understand better the H0 tension and what it implies for cosmology, before attempting a specific resolution within a specific beyond Lambda-CDM model.
There are also various “anomalies” hinting to breakdown of isotropy and homogeneity of the Universe at cosmological distances. In particular, there are hints of non-kinematical cosmic dipoles. We are developing the new framework of “Dipole Cosmology”.

In your career so far, at what point were you the most excited, and what were you excited about?
In my about 25 years of career, I have been excited about different things, e.g., various aspects of noncommutative (gauge) field theories and observational prospects of noncommutative spacetimes; proposing Tiny Graviton Matrix Model; gauge-flation as a theoretically well-motivated inflationary model; and more recently: physical implications of H0 tension & understanding black hole thermodynamics.

What is the biggest obstacle that is slowing down your research field right now?
Relative low quality of precise cosmological data, especially at low redshifts (z<2-3).

What role do you think a community network like CosmoVerse can play in developing theoretical astroparticle physics and cosmology?
It can (1) promote scientific exchange and debate; (2) provide a venue to develop new ideas; (3) facilitate scientific collaboration, and (4) help with the formation of a consensus and common picture on cosmological and astroparticle models.

What do you like and dislike about being a scientist?
Being a scientist is my passion. Of course, besides the personal aspects, science has strong community and social aspects. It is crucial to acknowledge this social aspect (it is not about liking or disliking ☺)

What non-physics interests do you have and want to share?
I compose music and play piano.

If you were not a scientist, what do you think you would be doing?
Good question, I have not really thought about it…….

What do you hope to see accomplished scientifically in the next 50 years?
Uncovering secrets of black holes and unveiling the physics of Dark Matter & Dark Energy.
Besides physics, quantum computers; finding ways to tackle global warming and climate change; understanding how our brain and cognitive system works; sociology and psychology becoming a “normal” part of our empirical sciences, just like physics.

In your view, what’s the most important challenge that humanity faces currently?
Environmental and climate challenges and precautions of very fast developing and spreading artificial intelligence.

What question would you have liked us to ask you, and what would you have answered?
Q: Does philosophy have a role to play in development of physics and cosmology?
A: In all aspects of theoretical sciences, more so in theoretical high energy physics and cosmology, it is important to have some awareness of the “overall picture” of the field. It is important to ponder upon whether and how we are making progress in the research field we are working on and what marks a progress.